1. Field of the Invention
The present invention relates to a still video adapter device having an image sensor for still video photography detachably mounted to a back portion of a camera body in place of a rear cover of the camera body, and particularly pertains to such a still video adapter device capable of interrupting or stopping the flash light emission in accordance with the amount of flash light projected from an electronic flash device to an object to be photographed, reflected by the object and incident through an objective lens of the camera body onto the image sensor.
2. Description of the Prior Art
A camera system has been proposed in a Japanese laid open utility model application No. 59-104132, wherein the camera system is composed of a camera housing including a photography optical system, a film photography unit including a film, a film transfer mechanism, a rear cover, a still video photography unit including an image sensor, a relay optical system for the image sensor and a recording device such as a floppy disk, the film photography unit and the still video photography unit being selectively mounted to the camera housing. In this prior art, the camera system is used for an original film type camera when the film photography unit is mounted to the camera housing and a still video camera when the still video photography unit is mounted to the camera housing. However this prior art does not disclose the construction or manner of controlling the amount of flash light when the still video photography unit is mounted to the camera housing.
Many cameras have been proposed wherein camera bodies are provided with a photocell for directly measuring a reflected flash light passing through an objective lens and reflected from the surface of a film and a flash light control circuit for integrating the output of the photocell and generating a signal instructing the interruption or termination of the flash light emission when the integrated amount reaches to a given level expected to provide a proper exposure. It may be considered to form a still video camera system by detachably mounting a still video adapter device having an image sensor to a back portion of the conventional camera body having such flash light control circuit, in place of a rear cover of the conventional camera, and to control the interruption of the flash light emission by means of the output of the flash light control circuit. However, in such still video camera system, the photocell for the flash light control circuit receives little light because a relay optical system for relaying the image formed at a film plane to the image sensor is disposed in the vicinity of the film plane and has very little reflectance, thereby causing the flash light control circuit to be inoperative.